Method for fabricating a DRAM capacitor having increased thermal and chemical stability

ABSTRACT

A method for fabricating a dynamic random access memory (DRAM) capacitor includes forming a first electrode film. The first electrode film comprises a conductive binary metal compound and a dopant. The dopant may have a uniform or non-uniform concentration within the first electrode film. A high-k dielectric film is formed over the first electrode film. A second electrode film is formed over the dielectric film. The second electrode film comprises a conductive binary metal compound and a dopant. The dopant may have a uniform or non-uniform concentration within the second electrode film. The dopants and their distribution are chosen so that the crystal structure of the surface of the electrode is not degraded if the electrode is to be used as a templating structure for subsequent layer formation. Additionally, the dopants and their distribution are chosen so that the work function of the electrodes is not degraded.

This document relates to the subject matter of a joint researchagreement between Intermolecular, Inc. and Elpida Memory, Inc.

FIELD OF THE INVENTION

The present invention generally relates to the field of dynamic randomaccess memory (DRAM), and more particularly to electrode processing forimproved DRAM performance.

BACKGROUND

Dynamic Random Access Memory utilizes capacitors to store bits ofinformation within an integrated circuit. A capacitor is formed byplacing a dielectric material between two electrodes formed fromconductive materials. A capacitor's ability to hold electrical charge(i.e., capacitance) is a function of the surface area of the capacitorplates A, the distance between the capacitor plates d, and the relativedielectric constant or k-value of the dielectric material. Thecapacitance is given by:

$\begin{matrix}{C = {\kappa\; ɛ_{o}\frac{A}{d}}} & \left( {{Eqn}.\mspace{14mu} 1} \right)\end{matrix}$where ∈₀ represents the vacuum permittivity.

The dielectric constant is a measure of a material's polarizability.Therefore, the higher the dielectric constant of a material, the moreelectrical charge the capacitor can hold. Therefore, for a given desiredcapacitance, if the k-value of the dielectric is increased, the area ofthe capacitor can be decreased to maintain the same cell capacitance.Reducing the size of capacitors within the device is important for theminiaturization of integrated circuits. This allows the packing ofmillions (mega-bit (Mb)) or billions (giga-bit (Gb)) of memory cellsinto a single semiconductor device. The goal is to maintain a large cellcapacitance (generally ˜10 to 25 fF) and a low leakage current(generally <10⁻⁷ A cm⁻²). The physical thickness of the dielectriclayers in DRAM capacitors could not be reduced unlimitedly in order toavoid leakage current caused by tunneling mechanisms which exponentiallyincreases as the thickness of the dielectric layer decreases.

Traditionally, SiO₂ has been used as the dielectric material andsemiconducting materials (semiconductor-insulator-semiconductor [SIS]cell designs) have been used as the electrodes. The cell capacitance wasmaintained by increasing the area of the capacitor using very complexcapacitor morphologies while also decreasing the thickness of the SiO₂dielectric layer. Increases of the leakage current above the desiredspecifications have demanded the development of new capacitorgeometries, new electrode materials, and new dielectric materials. Celldesigns have migrated to metal-insulator-semiconductor (MIS) and now tometal-insulator-metal (MIM) cell designs for higher performance.

Typically, DRAM devices at technology nodes of 80 nm and below use MIMcapacitors wherein the electrode materials are metals. These electrodematerials generally have higher conductivities than the semiconductorelectrode materials, higher work functions, exhibit improved stabilityover the semiconductor electrode materials, and exhibit reduceddepletion effects. The electrode materials must have high conductivityto ensure fast device speeds. Representative examples of electrodematerials for MIM capacitors are metals, conductive metal oxides,conductive metal silicides, conductive metal nitrides (i.e. TiN), orcombinations thereof. MIM capacitors in these DRAM applications utilizeinsulating materials having a dielectric constant, or k-value,significantly higher than that of SiO₂ (k=3.9). For DRAM capacitors, thegoal is to utilize dielectric materials with k values greater than about40. Such materials are generally classified as high-k materials.Representative examples of high-k materials for MIM capacitors arenon-conducting metal oxides, non-conducting metal nitrides,non-conducting metal silicates or combinations thereof. Thesedielectrics may also include additional dopant materials.

A figure of merit in DRAM technology is the electrical performance ofthe dielectric material as compared to SiO₂ known as the EquivalentOxide Thickness (EOT). A high-k material's EOT is calculated using anormalized measure of silicon dioxide (SiO₂ k=3.9) as a reference, givenby:

$\begin{matrix}{{E\; O\; T} = {\frac{3.9}{\kappa} \cdot d}} & \left( {{Eqn}.\mspace{14mu} 2} \right)\end{matrix}$where d represents the physical thickness of the capacitor dielectric.

As DRAM technologies scale below the 40 nm technology node,manufacturers must reduce the EOT of the high-k dielectric films in MIMcapacitors in order to increase charge storage capacity. The goal is toutilize dielectric materials that exhibit an EOT of less than about 0.8nm while maintaining a physical thickness of about 5-20 nm.

One class of high-k dielectric materials possessing the characteristicsrequired for implementation in advanced DRAM capacitors are high-k metaloxide materials. Titanium dioxide (TiO₂) is a metal oxide dielectricmaterial which displays significant promise in terms of serving as ahigh-k dielectric material for implementation in DRAM capacitors.

The dielectric constant of a dielectric material may be dependent uponthe crystalline phase(s) of the material. For example, in the case ofTiO₂, the anatase crystalline phase of TiO₂ has a dielectric constant ofapproximately 40, while the rutile crystalline phase of TiO₂ can have adielectric constant of approximately >80. Due to the higher-k value ofthe rutile-phase, it is desirable to produce TiO₂ based DRAM capacitorswith the TiO₂ in the rutile-phase. The relative amounts of the anatasephase and the rutile phase can be determined from x-ray diffraction(XRD). From Eqn. 1 above, a TiO₂ layer in the rutile-phase could bephysically thicker and maintain the desired capacitance. The increasedphysical thickness is important for lowering the leakage current of thecapacitor. The anatase phase will transition to the rutile phase at hightemperatures (>8000). However, high temperature processes areundesirable in the manufacture of DRAM devices.

The crystal phase of an underlying layer can be used to influence thegrowth of a specific crystal phase of a subsequent material if theircrystal structures are similar and their lattice constants are similar.This technique is well known in technologies such as epitaxial growth.The same concepts have been extended to the growth of thin films wherethe underlying layer can be used as a “template” to encourage the growthof a desired phase over other competing crystal phases.

Therefore, there is a need to develop a DRAM electrode which promotesthe growth of the rutile-phase in a TiO₂ dielectric layer duringformation of the dielectric layer. Such a DRAM electrode would enable aDRAM capacitor with high cell capacitance, small area, low leakagecurrent, and fast device speed.

Generally, as the dielectric constant of a material increases, the bandgap of the material decreases. This leads to high leakage current in thedevice. As a result, without the utilization of countervailing measures,capacitor stacks implementing high-k dielectric materials may experiencelarge leakage currents. High work function electrodes (e.g., electrodeshaving a work function of greater than 5.0 eV) may be utilized in orderto counter the effects of implementing a reduced band gap high-kdielectric layer within the DRAM capacitor. Metals, such as platinum,gold, ruthenium, and ruthenium oxide are examples of high work functionelectrode materials suitable for inhibiting device leakage in a DRAMcapacitor having a high-k dielectric layer. The noble metal systems,however, are prohibitively expensive when employed in a mass productioncontext. Moreover, electrodes fabricated from noble metals often sufferfrom poor manufacturing qualities, such as surface roughness, pooradhesion, and form a contamination risk in the fab.

Conductive metal oxides, conductive metal silicides, conductive metalnitrides, or combinations thereof comprise other classes of materialsthat may be suitable as DRAM capacitor electrodes. Generally, transitionmetals and their conductive binary compounds form good candidates aselectrode materials. The transition metals exist in several oxidationstates. Therefore, a wide variety of compounds are possible. Differentcompounds may have different crystal structures, electrical properties,etc. It is important to utilize the proper compound for the desiredapplication.

In one example, molybdenum has several binary oxides of which MoO₂ andMoO₃ are two examples. These two oxides of molybdenum have differentproperties. MoO₂ has shown great promise as an electrode material inDRAM capacitors. MoO₂ has a distorted rutile crystal structure andserves as an acceptable template to promote the deposition of therutile-phase of TiO₂ as discussed above. MoO₂ also has a high workfunction (can be >5.0 eV depending on process history) which helps tominimize the leakage current of the DRAM device. However, oxygen-richphases (MoO_(2+x)) degrade the performance of the MoO₂ electrode becausethey do not promote the deposition of the rutile-phase of TiO₂. Forexample, MoO₃ (the most oxygen-rich phase) has an orthorhombic crystalstructure.

Generally, a deposited thin film may be amorphous, crystalline, or amixture thereof. Furthermore, several different crystalline phases mayexist. Therefore, processes (both deposition and post-treatment) must bedeveloped to maximize the formation of crystalline MoO₂ and to minimizethe presence of MoO_(2+x) phases. The MoO_(2+x) phases may form duringthe deposition of the electrode and may not be evenly distributedthroughout the layer thickness. The MoO₂ electrode material may beformed using any common formation technique such as atomic layerdeposition (ALD), plasma enhanced atomic layer deposition (PE-ALD),atomic vapor deposition (AVD), ultraviolet assisted atomic layerdeposition (UV-ALD), chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), or physical vapor deposition (PVD).Typically, the MoO₂ electrode material must be annealed after formationto fully crystallize the film. Even if the anneal is performed under aninert gas such as nitrogen, the presence of MoO_(2+x) phases areobserved and the effective k-value of the TiO₂ dielectric subsequentlyformed on such an electrode is lower than desired.

Additionally, DRAM capacitor stacks may undergo various refinementprocess steps after fabrication. These refinement processes may includepost-fabrication chemical and thermal processing (i.e., oxidation orreduction). For instance, after initial DRAM capacitor stackfabrication, a number of high temperature (up to about 600 C.) processesmay be applied to complete the device fabrication. During thesesubsequent process steps, the DRAM electrode materials must remainchemically, physically, and structurally stable. They must maintain thestructural, compositional, physical, and electrical properties that havebeen developed. Furthermore, they should not undergo significantinteraction or reaction with the dielectric layer which may degrade theperformance of the DRAM capacitor.

Binary conductive metal oxide materials may not exhibit the requiredchemical and thermal stability under the various processing stepsimplemented during fabrication to be used as high quality capacitorelectrodes. Therefore, there is a need to produce an electrode systemthat exhibits good conductivity, a high work function, morphologicalproperties (i.e. roughness), and a crystal structure adequate fortemplating the preferred crystal phases of subsequently formed high-kdielectric materials, while simultaneously exhibiting good structural,compositional, physical, and electrical stability during subsequentthermal processing.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The drawings are not to scale and the relative dimensionsof various elements in the drawings are depicted schematically and notnecessarily to scale.

The techniques of the present invention can readily be understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a flow chart illustrating a method for fabricating aDRAM capacitor stack, in accordance with some embodiments of the presentinvention.

FIG. 2 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

FIG. 3 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

FIG. 4 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

FIG. 5 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

FIG. 6 illustrates a flow chart illustrating a method for fabricating aDRAM capacitor stack, in accordance with some embodiments of the presentinvention.

FIG. 7 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

FIG. 8 illustrates a simplified cross-sectional view of a DRAM capacitorstack fabricated in accordance with some embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention. Reference will now be made in detail to the subjectmatter disclosed, which is illustrated in the accompanying drawings.

FIG. 1 describes a method, 100, for fabricating a DRAM capacitor stack.The initial step, 102, comprises forming a first electrode layer.Examples of suitable electrode materials comprise conductive metaloxides, conductive metal silicides, conductive metal nitrides, andcombinations thereof. A particularly interesting class of materials isthe conductive metal oxides. Generally, these conductive metal oxidematerials also contain oxygen-rich components. The first electrodematerial further comprises the addition of a dopant. As used herein, a“dopant” is a minor constituent (generally <10 atomic %) of a layer ormaterial that is purposely added. As used herein, the dopant may beelectrically active or not electrically active. The definition excludesresidues and impurities such as carbon, etc. that may be present in thematerial due to inefficiencies of the process or impurities in theprecursor materials.

Dopants can be added to the conductive metal oxides to form ternarymaterial systems. Examples of these potential dopant materials includeSi, Al, Ge, or other metals (i.e. Sn, Ni, Ru, Ta, Re, Rh, Y, Zr, W,etc.). Additional dopants can be added to the ternary material systemsto form quaternary material systems. Examples of these potential dopantmaterials include Si, Al, metals, B, C, N (to form borides, carbides,nitrides), or combinations thereof.

In some embodiments, the dopant may be interspersed within the firstelectrode material as it is formed (i.e. co-deposited) or layered instep 102. The dopant may be formed as a unique layer during theformation of the electrode structure or may be co-deposited along withthe primary electrode material. If the dopant is formed as a uniquelayer, it may be deposited first, deposited in the middle of theelectrode structure, or may be deposited on top of the primary electrodematerial.

The dopants will tend to form ternary or quaternary material systemswith the two major components of the electrode material. Generally,these systems will exhibit better compositional and thermal stabilitythan their undoped binary counterparts. However, it is important thatthe addition of the dopant does not degrade the crystal structure of theelectrode material if the electrode material is to be used as atemplating layer for the formation of a desired dielectric crystalstructure. Furthermore, the addition of the dopant should not lower thework function of the electrode material and negatively impact theleakage current performance of the device.

It is further recognized that after the formation of the firstelectrode, an annealing process may be implemented in order to ensurethat the composition and crystalline phase of the first electrodematerial is suitable for templating subsequently deposited high-kdielectric materials. One example of such an annealing process isfurther described in U.S. application Ser. No. 13/084,666 filed on Apr.12, 2011, entitled “METHOD FOR FABRICATING A DRAM CAPACITOR” and isincorporated herein by reference.

Returning to FIG. 1, the next step, 104, comprises forming a dielectricmaterial on the first electrode layer. Optionally, the dielectricmaterial may undergo a post dielectric anneal (PDA) treatment (notshown). The next step, 106, comprises forming a second electrode layeron the dielectric layer. Optionally, the DRAM capacitor stack mayundergo a post metallization anneal (PMA) treatment (not shown).Examples of the PDA and PMA treatments are further described in U.S.application Ser. No. 13/159,842 filed on Jun. 14, 2011, entitled “METHODOF PROCESSING MIM CAPACITORS TO REDUCE LEAKAGE CURRENT” and isincorporated herein by reference.

Those skilled in the art will appreciate that each of the firstelectrode layer, the dielectric layer, and the second electrode layermay be formed using well known techniques such as ALD, PE-ALD, AVD,UV-ALD, CVD, PECVD, or PVD. Generally, because of the complex morphologyof the DRAM capacitor structure, ALD, PE-ALD, AVD, or CVD are preferredmethods of layer formation. However, any of these techniques aresuitable for forming each of the various layers discussed below. Thoseskilled in the art will appreciate that the teachings described beloware not limited by the technology used for the formation process.

In FIGS. 2-5 and 7-8 below, a capacitor stack is illustrated using asimple planar structure. Those skilled in the art will appreciate thatthe description and teachings to follow can be readily applied to anysimple or complex capacitor morphology. The drawings are forillustrative purposes only and do not limit the application of thepresent invention.

FIG. 2 illustrates a simple capacitor stack, 200, consistent with someembodiments of the present invention. Using the method as outlined inFIG. 1 and described above, first electrode layer, 202, is formed onsubstrate, 201. Generally, the substrate has already received severalprocessing steps in the manufacture of a full DRAM device. The firstelectrode may be any conductive material and includes dopant materialsup to about 10 atomic %. A class of materials of interest is theconductive metal oxides. Examples of the conductive metal oxides includethe conductive compounds of molybdenum oxide, tungsten oxide, rutheniumoxide, rhenium oxide, chromium oxide, rhodium oxide, iridium oxide,manganese oxide, tin oxide, cobalt oxide, or nickel oxide. A specificelectrode material of interest is MoO₂.

The dopant materials may be co-deposited with the bulk electrodematerial or may be introduced as one or more unique sub-layers. Forexample, if the electrode formation technology is ALD, AVD, or PE-ALD,the dopant precursor(s) can be introduced in the same pulse as the metalprecursor of the electrode material or the dopant precursor(s) can beintroduced in separate pulses. If the electrode formation technology isPVD, the dopant material(s) can be either co-sputtered or formed as aseparate layer during the formation of the electrode. Typically, thefirst electrode is annealed before proceeding to the formation of thedielectric material.

In the next step, dielectric layer, 204, would then be formed on thefirst electrode layer, 202. A wide variety of dielectric materials havebeen targeted for use in DRAM capacitors. Examples of suitabledielectric materials comprise SiO₂, SiO₂/Si_(x)N_(y), SiON, Al₂O₃, HfO₂,HfSiO_(x), ZrO₂, Ta₂O₅, TiO₂, SrTiO₃ (STO), SrBaTiO_(x) (SBT),PbZrTiO_(x) (PZT) or doped versions of the same such as Al:TiO₂. Thesedielectric materials may be formed as a single layer or may be formed asa hybrid or nanolaminate structure. Optionally, the dielectric layer maynow receive a PDA treatment. A specific dielectric material of interestis the rutile-phase of TiO₂.

In the next step, the second electrode layer, 206, is formed ondielectric layer, 204. The second electrode layer may be a conductivebinary metal compound material as described above, a metal, or acombination thereof. Optionally, the DRAM capacitor stack may nowreceive a PMA treatment. The remaining full DRAM device (not shown)would then be manufactured using well known techniques.

FIG. 3 illustrates a specific example of a simple capacitor stack, 300,consistent with some embodiments of the present invention. Using themethod as outlined in FIG. 1 and described above, first electrode layer,302, is formed on substrate, 201. Generally, the substrate has alreadyreceived several processing steps in the manufacture of a full DRAMdevice. One class of materials that is of interest as a DRAM electrodeis the conductive metal oxides. Examples of the conductive metal oxidesinclude the conductive compounds of molybdenum oxide, tungsten oxide,ruthenium oxide, rhenium oxide, chromium oxide, rhodium oxide, iridiumoxide, manganese oxide, tin oxide, cobalt oxide, or nickel oxide. As aspecific example, first electrode layer, 302, comprises a MoO₂ materialthat also contains one or more dopant materials. Specific dopantmaterials comprise Si, Al, or other transition metals. The goal is tomaximize the amount of MoO₂ present in first electrode layer, 302,because it has a distorted rutile crystal structure and would serve as agood template to promote the growth of the rutile-phase of a TiO₂dielectric material in a later step. A second goal is to ensure that thework function of the MoO₂ electrode material remains above ˜5.0 eV. Thepresence of oxygen-rich materials (MoO_(2+x)) is to be minimized becausethey generally do not promote the growth of the rutile-phase crystalstructure of the TiO₂ dielectric material and can decrease the workfunction. Typically, the first electrode is annealed before proceedingto the formation of the dielectric material.

In the next step, dielectric layer, 304, would then be formed on thefirst electrode layer, 302. In this example, a layer of TiO₂ that ispredominantly (>30% as determined by XRD) in the rutile-phase is formedas the dielectric layer, 304. The rutile-phase of TiO₂ growspreferentially over the anatase-phase due to the distorted rutile-phasecrystal structure of the underlying predominantly MoO₂ electrodematerial. The TiO₂ layer generally has a physical layer thicknessbetween 5 nm and 20 nm and exhibits a k value of >40. Optionally, thedielectric layer may now receive a PDA treatment.

In the next step, the second electrode layer, 306, is formed ondielectric layer, 304. The second electrode layer may be a conductivebinary metal compound material as described above, a metal, or acombination thereof. Advantageously, the second electrode is also doped.The dopant may be the same or different from the dopant used in thefirst electrode. In this example, the second electrode layer, 306,comprises a conductive binary metal oxide material. Optionally, the DRAMcapacitor stack may now receive a PMA treatment. The remaining full DRAMdevice (not shown) would then be manufactured using well knowntechniques.

FIG. 4 illustrates a simple capacitor stack, 400, consistent with someembodiments of the present invention. In this illustration, only a thinlayer of the conductive binary metal compound is used on top of apreviously deposited conductive base layer, 401, to form the firstelectrode. The thin layer of the conductive binary metal compound alsoincludes one or more dopant materials. The base layer may be a metal orhighly conductive material such as TiN, TaN, TiAlN, Al, Cu, W, WN or thelike. Using the method as outlined in FIG. 1 and described above, dopedthin first electrode layer, 402, is formed on base layer, 401.Generally, the substrate has already received several processing stepsin the manufacture of a full DRAM device. In this example, doped thinfirst electrode layer, 402, comprises a conductive metal oxide material.Examples of the conductive metal oxides include molybdenum oxide,tungsten oxide, ruthenium oxide, rhenium oxide, chromium oxide, rhodiumoxide, iridium oxide, manganese oxide, tin oxide, cobalt oxide, ornickel oxide. Typically, the first electrode is annealed beforeproceeding to the formation of the dielectric material.

In the next step, dielectric layer, 404, would then be formed on thedoped thin first electrode layer, 402. A wide variety of dielectricmaterials have been targeted for use in DRAM capacitors. Examples ofsuitable dielectric materials comprise SiO₂, SiO₂/Si_(x)N_(y), SiON,HfO₂, ZrO₂, Ta₂O₅, TiO₂, SrTiO₃ (STO), SrBaTiO_(x) (SBT), PbZrTiO_(x)(PZT) or doped versions of the same such as Al:TiO₂. These dielectricmaterials may be formed as a single layer or may be formed as a hybridor nanolaminate structure. Optionally, the dielectric layer may nowreceive a PDA treatment.

In the next step, the second electrode layer, 406, is formed ondielectric layer, 404. The second electrode layer may be a binary metalcompound material as described above, a metal, or a combination thereof.The second electrode layer, 406, may also be doped. Optionally, the DRAMcapacitor stack may now receive a PMA treatment. The remaining full DRAMdevice (not shown) would then be manufactured using well knowntechniques.

FIG. 5 illustrates a specific example of a simple capacitor stack, 500,consistent with some embodiments of the present invention. In thisillustration, only a thin layer of the doped conductive binary metalcompound is formed on top of a previously deposited conductive baselayer, 501, to form the first electrode. The base layer may be a metalor highly conductive material such as TiN, TaN, TiAlN, Al, Cu, W, WN orthe like. Using the method as outlined in FIG. 1 and described above,doped thin first electrode layer, 502, is formed on base layer, 501.Generally, the substrate has already received several processing stepsin the manufacture of a full DRAM device. In this example, doped thinfirst electrode layer, 502, comprises a MoO₂ and one or more dopants.Specific dopant materials comprise Si, Al, or other transition metals.The doped thin first electrode layer, 502, may have a thickness betweenabout 0.5 nm and 5 nm. One goal is to maximize the amount of MoO₂present in the doped thin first electrode layer, 502, because it has adistorted rutile crystal structure and would serve as a good template topromote the growth of rutile-phase TiO₂ dielectrics in a laterdeposition step. Typically, the first electrode is annealed beforeproceeding to the formation of the dielectric material.

In the next step, dielectric layer, 504, would then be formed on thedoped thin first electrode layer, 502. In this example, a layer of TiO₂that is predominantly (>30% as determined by XRD) in the rutile-phase isformed as the dielectric layer, 504. The rutile-phase of TiO₂ growspreferentially over the anatase-phase due to the distorted rutile-phasecrystal structure of the underlying predominantly MoO₂ doped thin firstelectrode material. The TiO₂ layer generally has a thickness between 5nm and 20 nm and exhibits a k value of >40. Optionally, the dielectriclayer may now receive a PDA treatment.

In the next step, the second electrode layer, 506, is formed ondielectric layer, 504. The second electrode layer may be a binary metalcompound material as described above, a metal, or a combination thereof.In this example, the second electrode layer, 506, comprises a dopedconductive binary metal oxide material. Optionally, the DRAM capacitorstack may now receive a PMA treatment. The remaining full DRAM device(not shown) would then be manufactured using well known techniques.

FIG. 6 describes a method, 600, for fabricating a DRAM capacitor stack.The initial step, 602, comprises forming a first electrode layer.Examples of suitable electrode materials comprise conductive metaloxides, conductive metal silicides, conductive metal nitrides, andcombinations thereof. A particularly interesting class of materials isthe conductive metal oxides. The first electrode material furthercomprises the addition of one or more dopants in a concentration up toabout 10 atomic %. In this embodiment, the dopant is not distributeduniformly throughout the first electrode layer. For example, theconcentration of the dopant can be adjusted so it is higher within thebulk of the first electrode layer than at the top surface of the firstelectrode layer. This may have a number of advantages. As discussedpreviously, the addition of the dopant increases the stability of theelectrode material during subsequent high temperature steps. Therefore,the dopant in the bulk of the first electrode material will increase thestability of the layer. However, the dopant must not significantly alterthe desired crystal structure of the top surface of the first electrodeand must not decrease the work function of the electrode. By reducingthe concentration of the dopant at the top surface of the electrode, thedopant will have a small effect on the crystal structure of the surfaceand the work function of the electrode.

The variation of the concentration of the dopant may assume many forms.In some embodiments, the concentration may vary in a linear fashionwhere it is highest at the bottom of the first electrode layer (i.e.closest to the substrate) and is lowest at the top surface (i.e. incontact with the dielectric layer). In some embodiments, theconcentration may be held at a constant level from the bottom of thefirst electrode layer to some distance into the electrode layer and thenabruptly decrease to a lower level for the remaining thickness. In thiscase, the concentration would vary in a step function manner. In someembodiments, the concentration may be lowest at both the top and bottomsurfaces of the first electrode layer and highest within the bulk of thelayer. Those skilled in the art will realize that these are just a fewexamples of how the variation of the concentration of the dopant can bedevised. Typically, the first electrode is annealed before proceeding tothe formation of the dielectric material.

Returning to FIG. 6, the next step, 604, comprises forming a dielectricmaterial on the first electrode layer. Optionally, the dielectric layermay now receive a PDA treatment. The next step, 606, comprises forming asecond electrode layer on the dielectric layer. The second electrodelayer may be a binary metal compound material as described above, ametal, or a combination thereof. The second electrode layer, 606, mayalso be doped. Optionally, the DRAM capacitor stack may now receive aPMA treatment.

FIG. 7 illustrates a simple capacitor stack, 700, consistent with someembodiments of the present invention. Using the method as outlined inFIG. 6 and described above, first electrode layer, 701/702, is formed onsubstrate, 201. Generally, the substrate has already received severalprocessing steps in the manufacture of a full DRAM device. The firstelectrode may be any conductive material and includes dopant materialsup to about 10 atomic %. The concentration of the dopant is non-uniformwithin first electrode layer, 701/702. This concept is illustratedschematically in FIG. 7 wherein layer 701 has a different dopantconcentration from layer 702. The variation of the concentration of thedopant may assume many forms as discussed previously. A specificelectrode material of interest is MoO₂.

The dopant materials may be co-deposited with the bulk electrodematerial or may be introduced as one or more unique sub-layers. Forexample, if the electrode formation technology is ALD, AVD, or PE-ALD,the dopant precursor(s) can be introduced in the same pulse as the metalprecursor of the electrode material or the dopant precursor(s) can beintroduced in separate pulses. If the electrode formation technology isPVD, the dopant material(s) can be either co-sputtered or formed as aseparate layer during the formation of the electrode. Typically, thefirst electrode is annealed before proceeding to the formation of thedielectric material.

In the next step, dielectric layer, 704, would then be formed on thefirst electrode layer, 701/702. A wide variety of dielectric materialshave been targeted for use in DRAM capacitors. Examples of suitabledielectric materials comprise SiO₂, SiO₂/Si_(x)N_(y), SiON, Al₂O₃, HfO₂,HfSiO_(x), ZrO₂, Ta₂O₅, TiO₂ SrTiO₃ (STO), SrBaTiO_(x) (SBT),PbZrTiO_(x) (PZT) or doped versions of the same such as Al:TiO₂. Thesedielectric materials may be formed as a single layer or may be formed asa hybrid or nanolaminate structure. A specific dielectric material ofinterest is the rutile-phase of TiO₂. Optionally, the dielectric layermay now receive a PDA treatment.

In the next step, the second electrode layer, 706/703, is formed ondielectric layer, 704. The second electrode layer may be a conductivebinary metal compound material and includes dopant materials up to about10 atomic %. The concentration of the dopant is non-uniform withinsecond electrode layer, 706/703. This concept is illustratedschematically in FIG. 7 wherein layer 706 has a different dopantconcentration from layer 703. The variation of the concentration of thedopant may assume many forms as discussed previously. Optionally, theDRAM capacitor stack may now receive a PMA treatment. The remaining fullDRAM device (not shown) would then be manufactured using well knowntechniques.

FIG. 8 illustrates a specific example of a simple capacitor stack, 800,consistent with some embodiments of the present invention. Using themethod as outlined in FIG. 6 and described above, first electrode layer,801/802, is formed on substrate, 201. Generally, the substrate hasalready received several processing steps in the manufacture of a fullDRAM device. One class of materials that is of interest as a DRAMelectrode is the conductive metal oxides. Examples of the conductivemetal oxides include the conductive compounds of molybdenum oxide,tungsten oxide, ruthenium oxide, rhenium oxide, chromium oxide, rhodiumoxide, iridium oxide, manganese oxide, tin oxide, cobalt oxide, ornickel oxide As a specific example, first electrode layer, 801/802,comprises a MoO₂ material that also contains one or more dopantmaterials up to a concentration of about 10 atomic %. The concentrationof the dopant is non-uniform within the first electrode layer, 801/802.This concept is illustrated schematically in FIG. 8 wherein layer 801has a different dopant concentration from layer 802. Layer 801 of thefirst electrode will have a higher concentration of the dopant. Layer802 of the first electrode will have a lower concentration of thedopant. Specific dopant materials comprise Si, Al, or other transitionmetals. The goal is to maximize the amount of crystalline MoO₂ presentin lightly doped electrode layer, 802, because it has a distorted rutilecrystal structure and would serve as a good template to promote thegrowth of rutile-phase of a TiO₂ dielectric material in a laterdeposition step. A second goal is to ensure that the work function ofthe MoO₂ electrode material remains above ˜5.0 eV. The presence ofoxygen-rich materials (MoO_(2+x)) is to be minimized because theygenerally do not promote the growth of the rutile-phase crystalstructure of the TiO₂ dielectric material. Typically, the firstelectrode is annealed before proceeding to the formation of thedielectric material.

In the next step, dielectric layer, 804, would then be formed on thefirst electrode layer, 801/802. In this example, a layer of TiO₂ that ispredominantly (>30% as determined by XRD) in the rutile-phase is formedas the dielectric layer, 804. The rutile-phase of TiO₂ growspreferentially over the anatase-phase due to the distorted rutile-phasecrystal structure of the underlying predominantly MoO₂ electrodematerial. The TiO₂ layer generally has a physical layer thicknessbetween 5 nm and 20 nm and exhibits a k value of >40. Optionally, thedielectric layer may now receive a PDA treatment.

In the next step, the second electrode layer, 806/803, is formed ondielectric layer, 804. The second electrode layer may be a conductivebinary metal compound material as described above, a metal, or acombination thereof. Advantageously, the second electrode is also dopedup to a concentration of about 10 atomic %. The dopant may be the sameor different from the dopant used in the first electrode. In thisexample, the second electrode layer, 806/803, comprises a conductivebinary metal oxide material. The concentration of the dopant isnon-uniform within the second electrode layer, 806/803. This concept isillustrated schematically in FIG. 8 wherein layer 806 has a differentdopant concentration from layer 803. Layer 806 of the second electrodewill have a higher concentration of the dopant. Layer 803 of the secondelectrode will have a lower concentration of the dopant. Specific dopantmaterials comprise Si, Al, or other transition metals. Optionally, theDRAM capacitor stack may now receive a PMA treatment. The remaining fullDRAM device (not shown) would then be manufactured using well knowntechniques.

The methods disclosed above may be used in the manufacture of asemiconductor device. The device will comprise a plurality of memorycells. Each memory cell will comprise at least one capacitor. Eachcapacitor will comprise a DRAM capacitor stack fabricated using theabove described methods. For example, a DRAM capacitor stack fabricatedin accordance with the present invention using a TiO₂ dielectric layerwith a k value of >40 and a physical thickness of 5-20 nm will have anEOT of less than 0.8 nm (from Eqn. 2 above), while providing adequatecharge retention characteristics. Moreover, the doped conductive metaloxide (e.g., MoO₂) based first electrodes of the present invention mayhave a work function greater than 5.1 eV leading to reduced leakagecurrent. Additionally, a DRAM capacitor stack fabricated using the abovedescribed methods of the present invention and having a physicalthickness of less than 20 nm is achievable via ALD, PE-ALD, AVD, UV-ALD,CVD, PECVD, or PVD.

Although various embodiments that incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

What is claimed:
 1. A method for fabricating a capacitor stack,comprising: forming a first electrode layer on a substrate, the firstelectrode layer comprising a first electrode material and a dopant;forming a dielectric layer on the first electrode layer; forming asecond electrode layer on the dielectric layer; and wherein the dopanthas a non-uniform concentration throughout the first electrode layer,and wherein the concentration of the dopant is lowest at a surface ofthe first electrode layer that is in contact with the dielectric layer.2. The method of claim 1, wherein the first electrode material comprisesone of conductive metal oxides, conductive metal silicides, conductivemetal nitrides, or combinations thereof.
 3. The method of claim 2,wherein the conductive metal oxide comprises one of molybdenum oxide,ruthenium oxide, rhenium oxide, tungsten oxide, rhodium oxide, iridiumoxide, chromium oxide, manganese oxide, tin oxide, cobalt oxide, nickeloxide, or combinations thereof.
 4. The method of claim 3 wherein theconductive metal oxide is molybdenum oxide.
 5. The method of claim 1wherein the dopant comprises at least one of Si, Al, Ge, or a transitionmetal.
 6. The method of claim 1 wherein the second electrode layerfurther comprises a second electrode material and a dopant.
 7. Themethod of claim 6, wherein the second electrode material comprises oneof conductive metal oxides, conductive metal silicides, conductive metalnitrides, or combinations thereof.
 8. The method of claim 7, wherein theconductive metal oxide comprises one of molybdenum oxide, rutheniumoxide, rhenium oxide, tungsten oxide, rhodium oxide, iridium oxide,chromium oxide, manganese oxide, tin oxide, cobalt oxide, nickel oxide,or combinations thereof.
 9. The method of claim 8 wherein the conductivemetal oxide is molybdenum oxide.
 10. The method of claim 6 wherein thedopant in the second electrode layer comprises one of Si, Al, Ge, or atransition metal.
 11. The method of claim 6 wherein the dopant in thesecond electrode layer has a non-uniform concentration throughout thesecond electrode layer.
 12. The method of claim 11 wherein theconcentration of the dopant is lowest at a surface of the secondelectrode layer that is in contact with the dielectric layer.